Victoripecten Beu & Darragh, 2001
BEU, A. G. & T. A. DARRAGH. 2001. Revision of southern Australian Cenozoic fossil Pectinidae (Mollusca: Bivalvia). Proceedings of the Royal Society of Victoria, 113: 1-205, figs. 1-67. [p. 121]
«Genus Victoripecten gen. nov.
Type species. Lentipecten victoriensis Crespin, 1950, Late Eocene to Early Miocene, southern Australia.
Diagnosis. Moderate-sized, weakly inflated, almost circular Adamussiini with weak radial sculpture on proximal area of RV anterior auricle, otherwise sculptured only with antimarginal ridgelets; with almost equal auricles, and only a shallow byssal notch remaining in adults, but a deeper notch and functional ctenolium present in specimens up to half-grown; dorsal margins of RV auricles serrated by growth ridges; weak, low radial costae developing late in ontogeny on RV posterior auricles (at least, in some specimens); several small, obvious, widely separated, deeply impressed gill-suspensor muscle scars present in the RV interior ventral to the adductor muscle scar.
Remarks. The Australian species for which Victoripecten is proposed has been included previously in Lentipecten Marwick, 1928 (type species: Pecten hochstetteri Zittel, 1864, Late Oligocene, New Zealand). The homeomorphy among these essentially smooth, saucer-shaped scallops, resembling Amusium externally but lacking internal rib carinae, is the most marked of all Australasian pectinid groups. During Eocene to Late Miocene times, when wanner than present sea temperatures prevailed around New Zealand and southern Australia, there was obviously very strong selection pressure by predators, driving scallops towards losing radial sculpture and becoming rapid, efficient swimmers (see ‘paradigms’ section in Johnson 1984). The Lentipecten shell form evolved repeatedly during this time, to the extent that many of the homeomorphs have been confusing and impossible to resolve until origins and time ranges were determined. The homeomorphs of Lentipecten in Australia and New Zealand are:
1. True Lentipecten hochstetteri (Zittel, 1864), the type species of Lentipecten Marwick, 1928; this is a Late Oligocene (Duntroonian) species of relatively large size (to at least 95 mm high) with strongly serrated RV auricle dorsal margins, an almost circular shape to slightly longer than high, and a hinge with very prominent dorsal teeth and the resilial teeth relatively long but very narrow and diverging at a much wider angle than in the Miocene ‘aff. Lentipecten’; apparently descended from Janupecten subteres (Marwick) by loss of its very weak radial sculpture (so Janupecten Marwick, 1928 is a synonym of Lentipecten Marwick, 1928; as first revisers, we select Lentipecten Marwick, 1928 as the valid name to be used by all authors who consider that Lentipecten Marwick, 1928 and Janupecten Marwick, 1928 are synonyms). Examination of Zittel’s (1864: pl. 11, fig. 5a) figured LV syntype of L. hochstetteri in Naturhistorisches Museum Wien (NHMV 1959/335/41) showed that this interpretation of the species is correct (seen, AGB, June 1998).
2. The Late Oligocene-Late Miocene ‘aff. Lentipecten sp. nov.’ of Maxwell (in Beu & Maxwell 1990: 144—145, pl. 10c, d), the species traditionally identified as L. hochstetteri, which is smaller (reaching c. 85 mm in height), is slightly taller than long, has only weakly serrate RV auricular dorsal margins, and has a hinge with the dorsal teeth a little less prominent than in L. hochstetteri, and with the resilial teeth much shorter and more steeply inclined than in L. hochstetteri. The origins of this species are unclear, but as some similar specimens are known from Oligocene rocks (ie., coeval with L. hochstetteri) it cannot have descended from L. hochstetteri', possibly it descended from ‘3.’, below.
3. A Bortonian (Middle Eocene) close homeomorph of the Oligocene-Miocene ‘aff. Lentipecten’, from the upper Waihao River, South Canterbury (R A. Maxwell, pers. comm.); much smaller than the Oligocene-Miocene specimens .(to c. 50 mm high, rather than 85 mm).
4. Duplipecten Marwick, 1928; Maxwell (in Beu & Maxwell 1990: 101, pi. 5d; Maxwell 1992: 64-65, pl. 3d—f) demonstrated that the late Middle and Late Eocene species D. parki (Marwick, 1942), although included in Lentipecten by Marwick (1942), is not a particularly close homeomorph of Lentipecten. It has the opposite relative valve inflation to L. hochstetteri, the auricles are set off from the disc by deep, undercut grooves, quite unlike the very shallow, obscure grooves of other Lentipecten homeomorphs (including Victoripecten), the proximal part of the disc, in particular, is sculptured with fine but obvious, regular commarginal ridgelets, and the hinge has a very different appearance as the teeth are much less obvious than in Lentipecten and the interior of the dorsal margin is dominated by large, thick, valve-abutting surfaces. D. parki is apparently descended from the slightly earlier Bortonian D. waihoaensis (Suter), which has obvious, low, wide radial costae developing relatively late in ontogeny on the LV disc.
5. ‘Lentipecten with a ctenolium’; a collection from the Bortonian (Middle Eocene) Island Sandstone at 10 Mile Bluff, north of Greymouth, Westland, New Zealand (IGNS, GS2600, GS2873) contains a few small specimens (to c. 45 mm high) that resemble Lentipecten in most characters (ie., in the lack of most pectinid characters!) but have a deeper byssal notch and retain a functional ctenolium in the largest specimens. No other specimens of these homeomorphs have been observed in New Zealand that bear a ctenolium, other than in small juveniles.
6. Victoripecten gen. nov., proposed here for Australian shells resembling the New Zealand Lentipecten homeomorphs listed above. Victoripecten resembles a larger version of homeomorph ‘5.’, as small (immature?) specimens from Late Eocene (Aldingan) rocks near Adelaide retain a functional ctenolium in the largest specimens seen, and younger, larger specimens have ctenolial teeth preserved in the groove between the RV anterior auricle and the disc until about half the adult size. Whether these might really be related phylogenetically to the New Zealand Middle Eocene species or were derived independently is unclear.
Whatever the relationships of Victoripecten, it is clear that its resemblance to Lentipecten is superficial, if nothing else because it appeared in Australia before the real Lentipecten had evolved in New Zealand, and the Australian species with an Eocene (Aldingan) to Early Miocene (Batesfordian) time range and with a functional
ctenolium until at least half adult height belongs in a genus distinct from Lentipecten. Indeed, one should obviously be highly sceptical of the placement of any extra-New Zealand taxa in Lentipecten. Even in New Zealand, , the limits and relationships of Lentipecten are complex, and any superficially similar taxa from the Northern Hemisphere are highly likely to be yet more unrelated homeomorphs. Victoripecten is proposed here, therefore, for the Australian species Lentipecten victoriensis Crespin, 1950. Despite the obvious impossibility of the Late Eocene to Early Miocene V. victoriensis having anything to do with the Late Oligocene Lentipecten hochstetteri in any phylogenetic sense, the only characters distinguishing V. victoriensis from Lentipecten hochstetteri, sensu stricto are its smaller size (to c. 70 mm high), the presence of a few very weak, faint radial costellae on the RV posterior auricle and on the anterior and posterior margins of the disc on some specimens, its rather more rounded (almost subcircular, rather than triangular) resilifer, its slightly longer and more steeply inclined resilial teeth, and the presence of a functional ctenolium until about half adult size. Complete specimens certainly resemble the nearcircular shape of L. hochstetteri, sensu stricto rather than the slightly taller shape of the Miocene ‘aff. Lentipecten’. Etymology. The generic name (Victoria + Pecten) refers both to the state in which the holotype of the type species was collected, and to the name of the type species. Gender masculine.»
ALAN GLENN BEU & THOMAS ALWYNNE DARRAGH, 2001
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Victoripecten victoriensis (Crespin); A. G. Beu & T. A. Darragh, 2001, Revision of southern Australian Cenozoic fossil Pectinidae, figures 42A-42E, 43A-43F.
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